Long chain fatty acid oxidation will be investigated in vitro and in vivo. Carnitine palmityltransferase A and B will be purified and characterized. The postnatal development of carnitine palmityltransferase A will be examined. The transport of palmitylcarnitine or a derivative across the mitochondrial inner membrane and its control will be measured. The effects of physiological, pathological and pharmacological alterations in fatty acid oxidation will be tested at an operational as well as enzymatic level in experimental animals. In addition, a protocol is outlined which will enable the monitoring of clinical situations involving abnormal fatty acid oxidation. A group of disease processes are defined which may possibly reflect abnormalities in lipid metabolism. The protocol contains initial screening methods using peripheral blood as well as detail studies that involve skeletal muscle biopsies.